Nano-structured Zinc-Chalcogenides are interesting for thermoelectric applications due to their low lattice thermal conductivity(κl). A simple theoretical model study has reported the κl cross-over of ZnS, ZnSe and ZnTe while going from bulk to nanoscale. We have performed a systematic first principles study of the Zinc-Chalcogenides to understand their thermal transport behaviour at the nanoscale. We have applied the Boltzmann transport equation in the relaxation time approximation to calculate the κl of Zinc-Chalcogenides. We find a κl cross-over between ZnS and ZnSe around 2-3μm and also show interesting κl ∼ 1W/m/K for ZnS nanostructures of 100nm size. We explain these findings in terms of the different contributions of phonon modes in these materials. Furthermore, the calculated κl is found to be strongly dependent on the volume and we explain the observed differences between LDA and GGA calculations. We compare further calculated thermal properties, such as thermal expansion coefficient, to experiment for validating our approach.
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